The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Recently, zinc oxide (ZnO) nanowires have been widely studied because of their superior electrical, mechanical, and optical properties. Various methods including vapor-liquid-solid (VLS) growth, chemical vapor deposition (CVD), electrochemical deposition (ED), and hydrothermal approaches have been employed for the synthesis of ZnO nanowires. However, the VLS, CVD, and ED methods require complicated and expensive equipment and can only be used under limited conditions, such as with single-crystalline substrates and at relatively high temperatures, e.g., 300° C. and above. Thus, hydrothermal synthesis is a more convenient and cost-effective approach for the large-scale preparation of well-ordered ZnO nanowire arrays at low temperatures. Recently, numerous hydrothermal growth methods of ZnO nanowires on various substrates have been vigorously explored and are continuously being evolved. Despite the benefits of hydrothermal synthesis of ZnO nanowires, the necessity of a crystalline ZnO seed layer limits the flexibility of this method due to the requirements of additional vacuum technology and high temperature processes.